Update README for 18.04
Update README for 18.04

proteusthemes/pt-ops,NicBeltramelli/trellis,buluma/trellis,proteusthemes/pt-ops,newtonne/trellis,NicBeltramelli/trellis,roots/bedrock-ansible,NicBeltramelli/trellis,newtonne/trellis,roots/bedrock-ansible,buluma/trellis,newtonne/trellis,partounian/trellis,partounian/trellis,pressbooks/trellis,jeffstieler/bedrock-ansible,buluma/trellis,jeffstieler/bedrock-ansible,partounian/trellis,pressbooks/trellis,partounian/trellis,NicBeltramelli/trellis,buluma/trellis,roots/trellis,jeffstieler/bedrock-ansible,roots/trellis,proteusthemes/pt-ops